The fabrication of flat panel displays involves the deposition of various films, including indium tin oxide (ITO) and metals, on large glass panels. The glass panels, which are typically rectangular, may have dimensions up to 450 mm by 550 mm or greater. ITO and metals can be deposited on the glass panels by sputtering from a target of the material to be deposited. In some cases, such as ITO, the target material may react with a gas, such as oxygen, in the sputtering chamber. Sputtering typically involves heating of the substrate and deposition of the desired film on the heated substrate. The substrate may be preheated in a separate chamber prior to sputtering.
Production systems for sputter deposition of films on glass panels should have automated substrate handling, a high throughput rate, minimum particulate contamination, small floor space requirements and high reliability.
One existing system for sputter deposition on flat panel displays is the so-called "inline" system, wherein substrates are moved along a linear or U-shaped path through various processing chambers. One disadvantage of such systems is that they require a large amount of floor space in the fabrication facility. In addition, such systems have limited flexibility in that only serial processes can be allowed; no parallel processing can be done.
Another existing system for sputter deposition of flat panel displays is the so-called "cluster tool". In the cluster tool, multiple processing chambers are positioned around a central chamber. The substrates are transferred from the central chamber into selected processing chambers. Existing systems have utilized a configuration where the substrate has a horizontal orientation and thus is subject to increased particulate contamination. Existing systems have also had a limited throughput rate.
All known systems for fabrication of flat panel displays have had one or more disadvantages, including yield loss due to particulate contamination, low throughput rates, high downtime due to frequent cleaning and target changes, inability to handle large panels, poor process monitoring, large floor space requirements and large clean room requirements. A critical element in such systems is the vacuum gate valve which isolates different vacuum chambers when it is closed and which permits substrates to be transported between chambers when it is open. The vacuum gate valve, in addition to providing a tight seal when closed, should operate in a short time, should be simple in construction and low in cost and should have a long operating life.